The proposed study constitutes the third phase of an ongoing project in which the immediate goal has been to provide data on the neuronal organization of the rabbit's visual system and in which the long range goal has been to promote a better understanding of evolution and of visual mechanisms in the mammals. In its first phase this project has yielded important information on the arrangement of the neuronal inputs to the thalamic, midbrain and pontine nuclei from the retina and visual cortical areas I and II (supported by granst NB 06253). In its second phase this project has been providing data on the associative and commissural fiber connections of visual cortical areas I and II of the rabbit (supported by gran EY 00607). In the proposed study the same established experimental approach will be used as was used in phases one and two of this project. Specifically, discrete surgical lesions varying in size and location will be produced in different cerebral cortical regions in rabbits; after postoperative survival periods allowing for the needed anterograde fiber degeneration, the animals will be killed and then the patterns of fiber degeneration in their brains studied in serial sections prepared by the Nauta and Nissl methods. Three types of cortical fibers will be investigated. First, the fibers that originate from the non-visual cortical areas, i.e., the cytoarchitectonic zones other than the peristriate, striate and occipitalis zones as defined by Rose (1931), and terminate in the primary optic nuclei in the rabbit. Second, the fibers that originate from the non-visual cortical areas and terminate in visual cortical areas I and II, i.e., the peristriate, striate and occipitalis zones of Rose (1931). Third, the fibers that arise from visual cortical areas I and II and end within the non-visual cortical areas.